No hot water from mixing valve

Hello. I bought a 'shower tower' over a year ago and finally hooked it up after gutting the bathroom and put it back together. The cold works great and the flow slows to a stop as I adjust all the way to hot. I removed the tower and have no problems with flow from supply lines. I've never taken a mixing valve apart. There are no markings on the valve to identify it. What's involved and any suggestions?
Mike